Such stents or implantable catheters to be introduced into a body cavity, a vessel or the like can be made from plastic or an inert metal, such as steel or nickel-titanium alloys. Such stents are also referred to as endovascular or endoluminal stents or endoprostheses. For example when dilating the ureter the stents are used in the prostate region in the case of benign prostate hyperplasia (BPH) or also in sclerotic blood vessels for dilating and keeping open the same. The stents have material areas and gaps between them. Thus, it is possible for the wall tissue of the organ kept open to grow round the stent. Stents can have a spiral construction or can be in the form of a helically wound coil. They can be made from woven or knitted wire or plastic material. Such stents can have memory properties, such as e.g. exist with certain nickel-titanium alloys (nitinol).
The problem of the invention is to ensure a secure anchoring of such a stent in the vessel to be dilated.
According to the invention the set problem is solved in the case of such a stent in that in the radially expanded state at least one front end has a greater radial extension than the remaining main body of the stent.
In the case of a stent, which is formed by ribs and free spaces left between the same, according to a preferred development of the invention in the vicinity of at least one front end of the stent the ribs have a greater length than corresponding ribs of the main stent body and in particular the length of the ribs in the front region can be 120 to 190% of the length of the ribs in the main stent region.
According to further preferred developments of the invention, in the front side areas the ribs extend radially further outwards than the ribs in the main stent area and the ribs in the front side area form a finite angle to the major axis of the stent.
The free spaces can either be diamond-shaped or honeycombed. The stent is preferably self-expanding and in a preferred development not solely due to elastic properties and introduction in a state under radial tension, but as a result of the fact that it is made from a memory metal.
In order to attain a greater bendability and flexibility of the stent, according to a further preferred development, between axially succeeding ribs are provided in part gaps and in part connecting areas. This is achieved by a higher flexibility than would be the case with a stent in which axially succeeding ribs were firmly interconnected in the connecting areas. There is also no cross-sectional deformation when bending under the action of vertical axial forces.
Due to the fact that the stent is constructed in single layer form, a high bendability is obtained without metal crossing points, such as is the case with knitted and braided structures and the like, which give rise to a greater material thickness. There can be a better growing in of the stent of the invention into the tissue. The risk of thromboses occurring, particularly in the vascular area is significantly reduced or virtually excluded.
In a preferred development, the connecting areas are circumferentially mutually displaced. This leads to the retention or obtaining of the desired axial strength (i.e. against compression and tension in the axial direction) in the case of bending resistance perpendicular to the axis.
According to further preferred developments the stent is made from a flat plate from which are cut slots for forming the gaps, the flat plates being connected together, particularly by welding, in the marginal areas after bending to a cylindrical contour and the free spaces are formed by slots after heat treatment.
Further advantages and features of the invention can be gathered from the claims and description of a preferred embodiment of the invention with reference to the drawings.